Linoleic acid (18:2) (LA) is transformed into gamma linolenic acid (18:3) (GLA) by the enzyme xcex946-desaturase. When this enzyme, or the nucleic acid encoding it, is transferred into LA-producing cells, GLA is produced. The present invention provides nucleic acids comprising the xcex946-desaturase gene. More specifically, the nucleic acids comprise the promoters, coding regions and termination regions of the xcex946-desaturase genes. The present invention is further directed to recombinant constructions comprising a xcex946-desaturase coding region in functional combination with heterologous regulatory sequences. The nucleic acids and recombinant constructions of the instant invention are useful in the production of GLA in transgenic organisms.
Unsaturated fatty acids such as linoleic (C18xcex949,12) and xcex1-linolenic (C18xcex949,12,15) acids are essential dietary constituents that cannot be synthesized by vertebrates since vertebrate cells can introduce double bonds at the xcex949 position of fatty acids but cannot introduce additional double bonds between the xcex949 double bond and the methyl-terminus of the fatty acid chain. Because they are precursors of other products, linoleic and xcex1-linolenic acids are essential fatty acids, and are usually obtained from plant sources. Linoleic acid can be converted by mammals into xcex3-linolenic acid (GLA, C18xcex946,9,12) which can in turn be converted to arachidonic acid (20:4), a critically important fatty acid since it is an essential precursor of most prostaglandins.
The dietary provision of linoleic acid, by virtue of its resulting conversion to GLA and arachidonic acid, satisfies the dietary need for GLA and arachidonic acid. However, a relationship has been demonstrated between consumption of saturated fats and health risks such as hypercholesterolemia, atherosclerosis and other clinical disorders which correlate with susceptibility to coronary disease, while the consumption of unsaturated fats has been associated with decreased blood cholesterol concentration and reduced risk of atherosclerosis. The therapeutic benefits of dietary GLA may result from GLA being a precursor to arachidonic acid and thus subsequently contributing to prostaglandin synthesis. Accordingly, consumption of the more unsaturated GLA, rather than linoleic acid, has potential health benefits. However, GLA is not present in virtually any commercially grown crop plant.
Linoleic acid is converted into GLA by the enzyme xcex946-desaturase. xcex946-desaturase, an enzyme of more than 350 amino acids, has a membrane-bound domain and an active site for desaturation of fatty acids. When this enzyme is transferred into cells which endogenously produce linoleic acid but not GLA, GLA is produced. The present invention, by providing genes encoding xcex946-desaturase, allows the production of transgenic organisms which contain functional xcex946-desaturase and which produce GLA. In addition to allowing production of large amounts of GLA, the present invention provides new dietary sources of GLA.
The present invention is directed to isolated xcex946-desaturase genes. Specifically, the isolated genes comprise the xcex946-desaturase promoters, coding regions, and termination regions.
The present invention is further directed to expression vectors comprising the xcex946-desaturase promoter, coding region and termination region.
Yet another aspect of this invention is directed to expression vectors comprising a xcex946-desaturase coding region in functional combination with heterologous regulatory regions, i.e. elements not derived from the xcex946-desaturase gene.
Cells and organisms comprising the vectors of the present invention, and progeny of such organisms, are also provided by the present invention.
A further aspect of the present invention provides isolated bacterial xcex946-desaturase. Isolated plant a6-desaturases are also provided.
Yet another aspect of this invention provides a method for producing plants with increased gamma linolenic acid content.
A method for producing chilling tolerant plants is also provided by the present invention.